A known magnetic disc (magnetic recording medium) to be used with a fixed magnetic disc device has a cross sectional structure as shown in FIG. 2. Specifically, a non-magnetic layer 2 made of Ni--P or Al, for example, is formed on a non-magnetic substrate 1 made of Al or glass, for example, to provide a non-magnetic base 11. A non-magnetic metal base layer 3, a hard magnetic layer 4 as described later, and a protecting layer 5 consisting essentially of C are successively laminated on the non-magnetic base 11, and a lubrication layer 6 is further formed on the protective layer 5. The hard magnetic layer 4 is made of CoCrTa or CoCrPtTa, for example, and has a coercive force (Hc) of 1600 Oe or higher.
To produce the magnetic disc as described above, the non-magnetic substrate 1 made of an aluminum alloy or a glass material or the like is finished with desired parallelism, flatness and surface roughness, and the non-magnetic layer 2 consisting of an Ni--P or Al film is formed on a major surface of the non-magnetic substrate 1 in a wet film-forming process, such as electroless plating, or a dry process, such as sputtering or deposition. The non-magnetic base 11 is heated to 150-200.degree. C., and the non-magnetic metal base layer 3, hard magnetic layer 4 and protective layer 5 are successively formed on the surface of the base 11 by a continuous sputtering method, while a dc bias of about 350V is applied to the base 11. The non-magnetic metal base layer 3 thus formed is made of Cr and has a film thickness of about 50 nm, and the hard magnetic layer 4 is made of a material, such as CoCrTa, which contains Co as a major component, and has a film thickness of about 30 nm, while the protective layer 5 contains C as a major component, and has a film thickness of about 10 nm. The protective layer 5 is then coated with a liquid lubricant containing fluorocarbon, which provides the lubrication layer 6 having a thickness of about 1 nm. The magnetic disc thus produced exhibits excellent mechanical characteristics, such as high strength and dimensional accuracy, without causing any problem when actually used, and also exhibits excellent magnetic characteristics. More specifically, the coercive force Hc is about 2000 Oe, and the product (Br.t) of the residual magnetic flux density (Br) and thickness t of the disc is about 150 G.mu.m. Further, the gradient (coercive force angle ratio S*) of the magnetic curve near the coercive force Hc is favorably about 0.93.
It is also proposed to use an alloy film as a base layer 3, which contains Cr as a major component, and Ti, V or the like, instead of the above-described base layer 3 made of Cr. This base layer 3 has a further increased coercive force Hc.
The magnetic recording medium is required to have a sufficiently high coercive force so as to achieve an increased rack recording density. In this connection, a magnetic recording disc having isotropic magnetic characteristics in which the coercive force in the circumferential direction of the disc is equal to the coercive force in the radial direction was evaluated in terms of its electromagnetic conversion characteristics, and relevant calculation proved that such a recording medium generates reduced noise, as reported in IEEE Trans. Magn. 29, ('93) 324. In this regard, it has been revealed that the base layer 3, when formed from a Cr film or an alloy film containing V or Ti as well as Cr as a major component, has a high coercive force Hc, but exhibits conspicuous anisotropic magnetic characteristics in which the coercive force in the circumferential direction of the disc is higher than that in the radial direction. Accordingly, undesirably large noise is generated by the recording medium having the non-magnetic metal base layer 3 in the form of the Cr film or alloy film as described above.